Synthetic methanol process



Sept. 6, 1932. w. J. EDMoNDs 1,375,754

V SYNTHETIC ETHHL PROCESS I File Dec. 13. 192,6

Patented Sept. 6, 1932 UNITED STATES PATENT ol-"FlcEl WILLIAM J.EDMONDS, OF TERRE HAUTE, INDIANA, .ASSIGN-OTR,v TO COMMERCIAL SOL- VENTSCORPORATION, OF LAND TERRE HAUTE, INDIANA, A CORPORATION F MARY-sYN'rHETIo mETHANoL'PnocEss Application iled December 13, 1928. SerialNo. 154,634.

' carbon monoxide, or carbon dioxide, or mixtures of the two.

I have now di covered that, in the case of the interaction oi carbondioxide andl hydrogen catalytically at elevated temperatures andpressures to produce methanol, optimum results are yobtained only whenthe carbon dioxide is present in extremely small proportion, that is,Iin a proportion to the hydrogen present which is far less than thecorrect theoretical proportion.

The combined reaction by which it has been assumed that methanol isproduced from car-l bon dioxide is one of the fourth order and isexpressed as follows:

BH2 CO2?- CHaOH H2O Some persons have further assumed that this combinedreaction might be separated into two simple equations, thus CO, HzdCO HCO zHzzioHsoH.

If the true reaction is assumed to be the simple reaction above shown,it follows from theoretical reasoning that the rate of reaction shouldbe at a maximum when theoretical proportions of carbon dioxidelandhydrogen are present in the gaseous mixture.

In connection with my experiments on the production of methanol frommixtures of hydrogen and carbon dioxide, I have passed gases containingvarious proportions of these ingredients over suitable catalytic agentsat temperatures of C-500 C., and-at pressures in excess of atmospheres.`All of the gases present are not reacted during one passage over thecatalyst and hence it is the practice to recirculate the residual gasesover the catalyst in cyclic fashion, nothing being removed from theprocess except the water` and methanol which are formed. To maintain thevolume of gas, which is continually diminished by the reaction, freshgas is constantly ladded to the system.

The method of manufacture of methanol from mixtures ofcarbon dioxide andhydrogen may be more clearly described with reference to Fig. 1 of thedrawing which shows a suitable apparatus in cross-section. .The'gasmixture to be reacted is supplied tothe process at the desired pressurethrough the makeup gas4 pipe A by the compressor (not shown). This gasmixes withlthe gas ofthe 4circulating' system at connection B, and the:mixed gases pass upward into the internal passage C of heat exchangerD.

While passing through the heat exchanger lthe gas is heated by thermalcontact with the from the methanol reaction which passes in reversedirection through the annular s ace E between the inner and outer wallsofp heat exchanger. From the exchanger the warmed gas passes downwardthrough pipe F into the converter (catalyst bomb) G. The gas passesdownward in the annular space between the inside wall of the converterand the walll of the catalyst basketH then rises upward through thecatalyst J and J through the perforated plate H forming the bottom ofthe basket H.

The .drawing shows the catalystr as separated into two sections, J and JSection J is designed tc act as a ,pre-catalyst or purifier, to destroyor absorb any catalyst poisons which may be present in the gas, and thusto preserve the catalytic activity of section J"v for the methanolreaction. The elevated temparat-ure in the converter G is largely mainhot gas the tained by the heat of reaction, but supple'- mentary heat isprovided for by means of elec.. tric heating elements K, K', embedded inan insulating jacket L which surrounds G'.

As the hot gas passes through the catalyst the Amethanol reactionoccurs, though all of the carbon oxides present in the` gas are notreacted at one passage'. The hot gas discharged from the converterthrough pipe M contains methanol vapors,l (water if carbon dioxide ispresent) and any reaction by-products formed, as well as unreactedcarbon oxides and hydrogen. This gas passes through the annular space E'of heat exchanger D giving up most of its heat to the incoming gas.

The partially cooled gas then passes from i the heat exchanger D viapipeN to the condenser O where it is cooled. The methanol thus obtainedin liquid form together with any water present is deposited in thereceiver P, from which the liquid may he removed through drain P. Theresidual, unreacted, gas rises through pipe Q, and passes to circulatingpump R.

The circulating pump R withdraws the residual gas from the receiver Pand combines make-up lgas is continually supplied under pressure throughpipe A.

I have discovered that when methanol is A produced from a mixture oftheoretical proportions of carbon dioxide and hydrogen, and even whenless than the theoretical proportion of carbon dioxide is employed thereis a formation of methane and carbn monoxide in the circulatinggasmixture and, further that free carbon is deposited in the appa--ratus. Also, the proportion of water found with the methanol when themixture is removed, by condensation, is much greater than that thatshould be formed by the methanol reaction.

From theresults thus attained it appears that there are a number ofprimary reactions occurring at different rates, rather than one or twosimple reactions.

The group of reactions which occur .in varying degrees is believed to beas follows (4) oo amazon. H20

(7) 2CD-C02 C.

It is thus Seenthat the desired course of the reaction-i. e. methanolproduction-is attained by the advantageous reactions 1, 5, and possibly6. On the other hand reaction 2 produces carbon monoxide and water. Thecarbon monoxide formed in reaction 2 may react advantageously withhydrogen to produce methanolaccording to reaction 5 or disadvantageouslyto produce carbon (Reaction from the apparatus, y

7 or methane (Reaction 4) Such carbon as is formed is, of course,removed from the process and Reaction 7 is practically irreversible. Thereactions, advantageous or disadvantageous, which produce water are alsolargely irreversible since water is constantly removed from the processtogether with the condensed methanol formed vlas the desired product.'

As illustrative of the conditions prevailing when it is attempted toreact carbon dioxide and hydrogen in theoretical proportions thefollowing typical experiment is cited.

A gas mixture comprising theoretical proportions of hydrogen and carbondioxide (i. e. approximately 25% carbon dioxide) was circulated over amethanol catalyst contain- -ing a mixture of zinc and chromium oxidesfor a period of 12 hours. IThe catalyst temperature was 420 C. and thegas pressure was 3500 pounds. After passing over the catalyst, the gaseswere cooled and the mix- `ture of methanol and water formed by thereaction was condensed under pressure and removed from the system. Theresidual (unreacted) gases were supplementedby .fresh gas andrecirculated. Under these conditions there was pro-duced 1.5 liters ofliquid per hour per liter of catalyst, the liquid showing methanol onanalysis where theoretically it should contain by volume. An analysis ofthe circulating gas after 12 hours of reaction showed the followingcomposition l Percent Carbon dioxide 21 Carbon monoxide- 12 Methane 5.2Hydrogen 6,1.8

gasescirculated over the catalyst was made after the process had been inoperation twelve hours and should he further remarked that prior gasanalyses showed that a practically static condition had been reached. Inother words, the proportions of methane and carbon monoxide found in thesystem were no longer increasing. The-p lowered yield of methanoll inthe condensate is attributable only to the disadvantageous -reactionspreviously mentioned, which, onl account of greater rapidity orselective action ermit the decomposition of carbon dioxide dhd ofhydrogen without a corresponding methanol production.

The results of the experiment show that while the use of a gas mixtureof theoretical proportions of carbon dioxide and hydrogen in themethanol process does not produce a theoretical quantity of methanol,still a more or less static condition is set up after a time in thecirculating system. `This is desirable, since it permits operationwithout constantly changing the proportions of the make-up- 105 Itshould he noted that this analysis of the v gas to maintain a definiteproportion of gases in, the circulating system.

By expiment, I have discovered that when the proportion of carbondioxide to hydrogen is greatly decreased the percentage of methanol inthe condensate approaches more closely the theoretical figure,(approximately Ywhich indicates that by the use of such proportions theundesirable side reactions are partially or wholly inhibited and thewaste of gases is thus avoided. I have discovered that When the gasmixture passing over the Vcatalyst comprises 1-5% carbon dioxide and99-95% hydrogen, the most'favorable results are obtained.

While the supplying of gases to the process in these favorableproportions produces the desirable result mentioned, it is y.obviousthat difficulties would'be encountered on the continued operation of theprocess. If a mixture of 3% carbon dioxide and 97% hydrogen isconstantly supplied to the process, all of the carbon dioxide will beconverted to methanol but a gneat excess of hydrogen will remainunreacted. If the make-up gas supplied to the process to maintain thepressure is of the same composition, the result occurring on continuedoperation will be a gradual diminution in the percentage of carbondioxide in thev system until it reaches an infinitesimal figure at whichpractically no methanol will be formed.

In the practice of my invention this diliiculty may be easily avoided.To adjust the process so that a gas of any desired proportion of carbondioxide will be present in the mixture passing over the catalyst, thecirculatory system in which the process operates is filled withsubstantially pure hydrogen gas at a pressure somewhat below thepressure desired for operation. The circulation of this gas through thesystem naturally produces no reaction of any kind. When this adjustmenthas' been accomplished a change is made in the gas supplied underpressure to the syste-m and instead of pure hydrogen, a

mixture of carbon dioxide and hydrogen in the proportions theoreticallyrequired to make methanol is supplied to the system. This gas blendswith the pure hydrogen in the system and at the point where the gasespass the catalyst, the percentage of carbon dioxide is very small.

Since under the favorable reaction conditions thus effected the carbondioxide is converted almost entirely to methanol, the

amount of carbon dioxide disappearing from wat the system is directlyproportionate to the amount of hydrogen disappearing. Consequently ifthe gas mixture of theoretical proportions is constantly supplied asmake-up gas at a rate which maintains a constant pressure in the system,methanol and water are continually produced, and the composition 'ofther gas in the circulating system remains `unchan ed. In thismanner amost desirable statlc condition is set up inwhich a gas of one unvaryingcomposition remains in the circulating system andanother gas of adifferent but also unvarying composition is supplied to the system atthe same rate at which the theoretical mixtureof methanol and water isformed.

Instead of filling the circulating system with pure hydrogen at apressure approximating the pressure desired for the reaction, the gasplaced in the circulating system may contain some carbon dioxide. Thismay be accomplished either by iilling the system at the pressure ofoperation with a gas containing a predetermined quantity o fcarbondioxide, or by passing pure hydrogen into the system until only part ofthe pressure desired for operation has been attained, and/ then adding agas containing theoretical prportions of carbon dioxide and hydrogen,uni til the desired pressure has been attained. In this manner it `ispossible to adjust the gas in the circulating system to any desiredratio of carbon dioxide to hydrogen. Then, to operate-the process, themake up gas of'theoretical proportions is supplied to the system and asimilar static condition may be attained.

However if this adjustment produces a circulating system gas whichcontains more than 5% of carbon dioxide, a loss of gases j will occuronaccount of the undesirable reactions previously described. Largequantities of methane and carbon monoxide will be built up in the systemand while continued operation of the process will finally produce astatic ycondition in that the composition of gases in the circulatingsystem becomes unchanging in composition, the yield of methanol will bemuch lower than that theoretically obtainable.

Typical results obtained by this method of operation are indicated inthe following tab'- ulations Tablei I Analysis of gaes rirculating lover ca a ys sa Yield' as Saa:

COI CO CH4 Hz Liters of condensate per hour per liter of catalyst. iPercent by volume of methanol in condensate (remainder bein er). Hoursof operation at time of test.

In the experiments above reported, a pressure of 3500 pounds wasemployed, and the make-up gas supplied to the process was a mixture ofcarbon dioxide and hydrogen of approximately the theoretical proportionsrequired for methanol production. The temperature employed was 420 C. ineach case,

Si)A

and a vspace velocityA of 100,000 was employed. The

present in the circulating 'system before the methanol fore .the make-upgas was supplied to the process. 'l

Table I indicates that as the percentage of carbon dioxide in thecirculating gases was reduced from 11% to 2%, the per cent .of

methanol inthe condensate was increased from 60.5% to 66%. Thepercentages of methane and carbon monoxide present in the circulatingsystem are also reduced as thel result of the dimunition in carbondioxide. The fact that in Experiment Lirthe percentage of carbonmonoxide in the circulatinggases i exceeded the percentage of carbondioxide is parently the methane of no'importance, for the production ofa larger percentage of methanol 1n the condensate than was obtained inthe other expenments indicates that disadvantageous side reactions werediminished in activity. Ap-

and carbon monoxide were formed during the irststages of reaction-beforea static condition in the circulat- I bon dioxide in t. e circulatingsystem, gave ing system was attained. t

While 'Experi ent 2, employing 6.5% carthe largest yield of condensateper hour, this i is not the consideration of prime importance in theeconomy of the process. Any desired yield of condensate per hour may beobtained by increasing the apparatus and the amount of catalystemployed. The greatest economy and eiiiciency of operation is attainedwhen all of the gases removed from the process enter into the productionof the theoretical "mixture of methanol and water,'rather thandisadvantageous side reactions. For ex ample, the same volume ofcondensate per hour as was obtained in Experiment 2 may be obtained vinExperiment 4 by merely doubling the amount of catalyst employed, andmodifying the apparatus accordingly.

Table II Analysis of gasesl ctircuiating over 08 8 YS Time of Expt.Puril No. Yield e gra CO3 C0 CH( H:

Litera oi condensate per hour per liter o( catalyst. Percent by volumeoi methanol in condensate (remainder being water).

" Hours of operation at time ot test.

In the experiments reported in Table II a pressure of` 3500 pounds wasemployed and the make-up gas supplied to the process was a mixture ofcarbon dioxide and hydrogen -of approximately the theoreticalproportions required for methanol production. In

A variance in results shown -inthe experiments is due tof varlance 1nthe gas reaction was started--that is be"-` employed (390 C.)

each case a tem erature of 390 C. and a space velocity o 60,000 wasemployed.

Table II confirms favorable effect obtained by employing a gas mixturecontaining only a small proportion of carbon dioxide.

is a more favorable bne, the purity of the methanol thus vproduced isgreater; for example, Experiment v7 produced a condensate containingpractically'the theoretical proportions of methanol and water.

Table I in showing the Since the temperature My process is in no waydependent'on the use of a specific catalyst. In general, any

catalyst suitable for synthetic methanol roduction may be employed inthe rocess, t ese v catalysts ordinarily consisting o mixtures ofmetallic oxides such as are described, for example, in United StatesPatents 1,558,559; 1,608,643; and 1,609,593; and English Patents 229,714and 229,715.

My invention is in no way dependent, for its operation, on theemployment of the vspecific apparatus disclosed in the drawing and iti's obvious that many manipulative variations might be made withoutdeparting from the spirit thereof.

My invention is not dependent lonthe maintenance of a static condition4within the circulating system whereby make-up gas of theoreticalproportions is passed into a sys# tem of circulating gas originallycomposed vof substantially'pure hydrogen, this process being the subjectmatter of application Serial No. 154,635, filed December 13th, 1926.

For example, Ithe favorable result attendant on the use of a very smallproportion of carbon dioxide in the methanol synthesis may beaccomplished by passing a gas of the proportion of 3% carbon dioxide and97% hydrogen into the-.system under pressure, circulating it to makemethanol, gradually adding carbon dioxide -to the system to replenishthe carbon dioxide converted to methanol,

and, occasionally adding some hydrogen to maintain the correctproportions of mate'- rials in the circulating gas. ly, the circulatingsystem may be dispensed with and a gas of thev correct proportions maybe passed through a number ofcatalyst beds in series, pressure beingmaintained in the system, so that a preponderance of the gas enteringthe system is converted to methanol and water by one passage, theresidual gases bemg recovered for use in an- Or, alternativeand 99-95%hydrogen' over said catalyst, circulating said gas mixture to makemethanol, adding hydrogen and carbon dioxide to the system to replenishthat consumed, the

amount of carbon dioxide in said system being always maintained belowapproximately 5%.

' 2. In :the process of manufacturing methbon dioxide in the presence ofa catalyst and under-the iniiuence of elevated' pressure andtemperature, the steps which comprise passing a gas consisting ofapproximately 3% lcarbon dioxide and 97% hydrogen over said catalyst,circulating said gas mixture to make anol by^the interaction of hydrogenand carmethanol, gradually adding carbon dioxide 4 to the" system toreplenish the carbon dioxide converted to/methanol, adding sulicienthydrogen to the system to maintain the correct proportions of materialsin the circulating gas, the amount of carbon dioxide in said systembeing maintained at approximately 3% l 3. In thev process ofmanufacturing methanol by the interaction of hydrogen and carbondioxide'in the presence of a catalyst and under the iniiuence ofelevated pressure and temperature, the steps which comprise passinga gasconsisting of 1-5% carbon dioxide and 99-95% hydrogen over saidcatalyst, adding to the residual gases hydrogen and carbon dioxide insucient uantitiesto replenish the carbon dioxide an sumed, the amount ofcarbon dioxide in said ystem being maintained below approximate- 4. Inthe process of manufacturing methanol by the interaction of hydrogen andcarbon dioxide in the presence of a catalyst and under the influence ofelevated pressure and temperature, the steps which comprise passing agas consisting of approximately 3% carbon dioxide and 97% hydrogen oversaid catalyst, adding to the residual gases hydrogen and carbon dioxidein tities to replenish .the carbon drogen consumed, the amount ofcarbon-dioxide in said system being maintained at approximately 3%.

In' testimony whereof I aiiix m si WILLIAM J. EDKIO ature.

hydrogen consufiicientquandioxide and hy-

